ATtiny167-ESSZ datasheet(51/282 Pages) ATMEL

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7728D–AVR–07/09

ATtiny87/ATtiny167

Figure 6-3.

MCU Start-up, RESET Extended Externally

6.1.4

External Reset

An External Reset is generated by a low level on the RESET pin. Reset pulses longer than the

minimum pulse width (see Table 22-3 on page 246) will generate a reset, even if the clock is

not running. Shorter pulses are not guaranteed to generate a reset. When the applied signal

reaches the Reset Threshold Voltage – V

RST – on its positive edge, the delay counter starts

the MCU after the Time-out period – t

TOUT – has expired. The External Reset can be disabled

by the RSTDISBL fuse, see Table 21-4 on page 226.

Figure 6-4.

External Reset During Operation

6.1.5

Brown-out Detection

ATtiny87/167 has an On-chip Brown-out Detection (BOD) circuit for monitoring the Vcc level

during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be

selected by the BODLEVEL Fuses (See ”BODLEVEL Fuse Coding” on page 247.). The trigger

level has a hysteresis to ensure spike free Brown-out Detection. The hysteresis on the detec-

tion level should be interpreted as V

BOT

+ =VBOT +VHYST /2andVBOT– =VBOT -VHYST /2.

When the BOD is enabled, and Vcc decreases to a value below the trigger level (V

BOT

– in Fig-

ure 6-5), the Brown-out Reset is immediately activated. When Vcc increases above the trigger

level (V

BOT

+ in Figure 6-5), the delay counter starts the MCU after the Time-out period tTOUT

has expired.

The BOD circuit will only detect a drop in Vcc if the voltage stays below the trigger level for lon-

ger than t

BOD given in Table 22-6 on page 247.

RESET

TIME-OUT

INTERNAL

RESET

tTOUT

VRST

VPOR

VCCRR

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